In completing a well, perforations are often extended into the formation surrounding a wellbore to enable communication of well fluids between the formation and the wellbore. Perforation is accomplished by use of perforating guns that are run into the wellbore from a well surface. Such perforating guns typically include shaped charges that, when initiated, produce perforating jets that cut through a casing or liner and extend perforating tunnels into the surrounding formation. The shaped charges are typically connected to a detonating cord, which is in turn connected to a detonation assembly (or firing head). To activate the perforating gun, an input signal (such as an electrical signal, optical signal, pressure pulse signal, mechanical signal, or another signal) is provided to the detonation assembly, which causes initiation of the detonating cord. A detonation wave traveling down the detonating cord causes detonation of the shaped charges.
Explosives can also be used to perform other well operations, such as setting packers, activating pipe cutters, and so forth. An issue associated with initiating explosives in a wellbore is the presence of a high hydrostatic pressure inside the wellbore, particularly when detonation assemblies to initiate the explosives are exposed to the wellbore pressure. Hydrostatic pressures of as high as 20,000 psi (or even higher) in a wellbore is not uncommon. The presence of high pressure in a wellbore can make explosive detonation less reliable, and the ballistic transfer between multiple explosive elements less reliable. In the presence of high pressure, explosive elements such as a detonating cord or a booster explosive are compacted, which causes the explosive elements to become desensitized.
In conventional detonating assemblies of perforating guns, a sealed housing is often provided, with the sealed housing containing a detonator. The inner chamber of the sealed housing is at ambient pressure, which allows reliable initiation of the explosive in the detonator that is located in the sealed housing. With a conventional sealed housing, a pressure barrier is usually used between the detonator and another explosive component (such as a booster explosive or a detonating cord) that is to be initiated by the detonator. The pressure barrier prevents entry of wellbore pressure into the inner chamber of the sealed housing. The pressure barrier often is in the form of a thin wall of the housing. Initiation of the detonator causes the barrier to be ruptured to enable the detonation to be transferred from the detonator to the explosive component on the other side of the barrier. The pressure barrier tends to reduce the explosive energy that can be directed from the detonator to the explosive element through the barrier. As a result, the transfer of explosive energy from the detonator to the other side of the barrier may not reliably detonate the explosive element.